If your organisation is still running classic SharePoint publishing sites, this is one update you really shouldn’t ignore.
Between 15 September 2025 and 15 March 2026, Microsoft is rolling out significant changes to SharePoint Online. Nothing is being switched off overnight — but Microsoft is making it very clear that the future of SharePoint is modern.
Let’s break down what’s changing, why Microsoft is doing it, and what IT teams should be doing now to stay ahead of the curve.
What’s changing in SharePoint Online?
1. Custom scripting will be disabled on classic publishing sites
From 15 September 2025, Microsoft will begin disabling custom scripting by default on all classic publishing site collections.
In practical terms, this means:
- DenyAddAndCustomizePages will be set to True
- You won’t be able to add new scripts using Script Editor or Content Editor web parts
- Existing scripts already embedded will continue to work (for now)
- New customisations, master pages, or page layouts won’t be possible without temporarily re-enabling scripting
Classic sites won’t break — but they’ll become far more static.
2. You won’t be able to create new classic publishing sites
That means:
- No new Publishing Portals or Publishing Sites
- No Enterprise Wikis or classic Search Centres
- Publishing features can’t be activated on modern sites anymore
- Attempts to create classic publishing templates via UI, API, or PowerShell will be blocked by default
3. Property bags can now be managed without enabling scripts
There is one genuinely helpful change.
Microsoft is introducing a new setting that allows admins to update site property bags without turning custom scripting back on:
AllowWebPropertyBagUpdateWhenDenyAddAndCustomizePagesIsEnabled
This can be configured at tenant or site level and means admins can safely manage metadata via PowerShell without opening the door to unrestricted scripts. It’s a small but important improvement in governance.
4. Temporary PowerShell opt-outs (until March 2026)
Microsoft knows not everyone can modernise overnight, so there’s a grace period.
Between September 2025 and 15 March 2026, tenant admins can use PowerShell to:
- Delay script disablement tenant-wide
- Temporarily re-enable scripting on a specific site (for 24 hours)
- Allow creation of new classic publishing sites if absolutely necessary
The key thing to note: The tenant-wide delay expires on 15 March 2026. After that, there’s no extension.
What’s not changing (yet)
Let’s clear up a common concern.
- Existing classic publishing sites are not being deleted
- They will continue to work as they do today
- Subsites can still be created under existing publishing site collections
However, these sites are now effectively isolated. You can keep them running, but you can’t grow them, and long-term support is clearly winding down.
Think of this as Microsoft putting classic SharePoint into maintenance mode.
Why is Microsoft doing this?
Security first
Custom scripting has long been a security headache. Ungoverned JavaScript can introduce vulnerabilities, performance issues, and compliance risks. Disabling it by default aligns with Microsoft’s wider M365 security strategy.
Modern SharePoint is easier (and better supported)
Modern sites are responsive, mobile-friendly, faster, and far easier for users to maintain. Many things that once required custom code now come out of the box.
Less technical debt
Classic publishing is legacy technology. Maintaining it adds complexity and risk — both for Microsoft and customers. Retiring it allows focus on modern, cloud-first capabilities.
A more consistent user experience
Mixing classic and modern SharePoint creates confusion. Microsoft wants one consistent experience that integrates cleanly with Teams, Viva, and the rest of Microsoft 365.
The message is clear: modern SharePoint isn’t optional anymore.
What does this mean for IT admins?
If you’re responsible for SharePoint, this change has real implications.
- Customisations on classic sites will be frozen
- New classic publishing sites won’t be an option
- Admins will need to manage temporary opt-outs carefully
- Users may be confused when familiar options disappear
Most importantly, doing nothing is no longer a viable strategy.
What should you be doing now?
1. Audit your classic SharePoint estate
Identify:
- All classic publishing sites
- Any custom scripts, layouts, or legacy components
- Business-critical functionality
Microsoft’s Modernization Scanner is extremely helpful here.
2. Talk to site owners early
Explain:
- What’s changing
- What will stop working
- Why modern SharePoint is the long-term answer
Clear communication now avoids panic later.
3. Plan modern replacements
Some sites will migrate easily. Others may need:
- Modern communication sites
- SPFx web parts
- Power Apps or Power Automate flows
Prioritise business-critical areas first.
4. Use opt-outs sparingly
The PowerShell delays are a safety net — not a solution.
If you rely on them, make sure there’s a clear exit plan before March 2026.
5. Invest in modern SharePoint adoption
Run pilots. Train users. Show them what modern SharePoint can do.
Most resistance disappears once people see:
- Cleaner layouts
- Easier editing
- Better mobile experience
- Fewer “IT-only” dependencies